Control of separately-excited generators.



No. 866,081. PATENTED SEPT. 17, 1907. G. STERN. CONTROL OF SEPARATELY EXCITED GENERATORS.

APPLIOATION FILED JAN. 23, 1907 W/Zinesses: /r7 ventor' UNITED STATES PATENT OFFICE.

GEORG STE :tN, OF BERLIN, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY,

A GORPORATION OF NEW YORK.

CONTROL OF SEPARATELY-EXCITED GENERATORS.

no. seo,oe1.

Specification of Letters Patent.

Patented Sept. 1'7, 190?.

Application filed January 28, 1907. $erial No. 353,626.

To all 1.0710112. it may concern:

lie it known that I, Gnouo STERN, a subject of the King 01' Prussia and Emperor 01 Germany, residing at Berlin, Germany, have invented certain new and uselul lmprovements in Control of Separate]y-Excited Generators. of which the following is a specification.

My invention relates to the control 01' separatelycxcited generators, and its object is to provide a novel method ol ccnitrol, whereby the generator voltage may be reduced absolutely to zero.

Separately-excited generators have been frequently employed heretol'ore [or purposes ol motor-control where a wide range ol speed is required. By supplying the motor armature lrom a separately-excited gen orator and varying the field-strength of the generator, the voltage supplied to the motor armature may be varied over wide limits, so as to vary the s reed correspondingly, while maintaining a constant field-excitation on the motor. Such control systems heretoiore have not been arranged. to reduce the generator voltage absolutely to zero. Even when the hold circuit of the generator is broken, the generator produces a voltage due to residual magnetism, which, unless the armature circuit is broken, supplies a current to the motor, so that ii the motor is lightly loaded it may continue to turn slowly. Even ii an automatic brake is provided for stopping the motor when the generator field-circuit is broken, the generator armature will be short-circuited through the ohmic resistance of the motor armature, and the voltage due to the residual magnetism may be suflicient to cause an appreciable current to flow in the short-circuit. The flow o'l' current due to residual magnetism may of course be avoided by lu'eaking the armature circuit, but this is .l'requently undesirable and complicates the control.

By my invention the generator-voltage may be reduced absolutely to zero, so that the armature circuit may be maintained. closed at all times.

My invention consists in not only disconnecting the generator field from the separate exciter, when it is desired to reduce the generator voltage to zero, but also in connecting the generator field in shunt to its armature in such a way that the voltage due to the residual magnetism supplies a current to the field, which acts to annihilate the residual magnetism.

My invention further consists in arranging the controlling switch for producing this connection in its offposition.

My invention will best be understood by reierence to the accompanying drawing, which shows diagrammatically a control system arranged in accordance with my invention.

In the drawing A represents the armature and a the [ield of a separatelyexcited generator. This generator may be driven in any suitable manner, as, for instance, by the shunt motor B supplied from the constant potential mains b.

O represents the separate exciter [or the generator, and may consist o[ a small generator mounted on the shalt oi the main generator, as shown, or oi any other suitable source of current, such as a battery.

D represents the armature and (Z the field of a motor supplied from the generator A. The motor armature D is permanently connected to the terminals of the generator armature A, while the motor field (1 is supplied with a constant excitation from the exciter O.

E represents a controlling switch, which is arranged to connect the generator field a to the exciter G. to vary the current supplied to the generator field, and in its off-position to connect the generator lield a in shunt to its armature.

F represents a variable resistance arranged to be connected in series with the generator field a by the switch F.

The switch E is shown in its oft-position. N eglecting for the moment the connections established in this position, it will be seen that ii the switch E is moved in either direction, for instance, toward the right, a circuit will be closed iron} the upper terminal oi exciter O through resistance F, contacts 1, 2, 3, l, 5, 6 and 7, through field a, and through contacts 8, 9, 10 and 11, to the lower terminal of exciter G. The generator field a is thus connected to the exciter with all of resistance F in series. As the movement 01' the switch is continued, resistance F is gradually cut out of circuit. If the switch E had been moved in the opposite direction lrom off-position, the same circuit connections would have been established, except that the connections of the hold a would have been reversed, so that the voltage delivered by the generator A would have been reversed. Now, if the switch E is returned to its off-position, the generator held a is disconnected from the exciter C and is connected in shunt to the generator armature A. This circuit may be traced from the upper brush of armature A to contacts 12, 13, 6 and 7, through generator field a, and contacts 8, 9, l4 and 15, to the lower brush to armature A. When this connection is made, the armature voltage due to residual magnetism will send a current through the field winding, which will tend to increase or diminish the armature voltage. When the connection is proparmature voltage completely to zero.

all current supplied to the motor is as effectually stopped as if the armature circuit were broken; so that no switch in the armature circuit is required.

What I claim as new and desire to secure by Letters Patent oi the United States, is:-

1. The method or controlling a separately-excited generator, which consists in supplying a variable current to the generator held from an external source to vary the voltage delivered by said generator, and in connecting the generator field in shunt to its armature to reduce the generator voltage.

2. The method or reducing to zero the voltage or a separately-excited generator, which consists in disconnecting the generator lield from the separate cXciter and connect'in it in shunt to the generator armature to annihilate the residual magnetism of the field.

ll. in combination with a separately-excited generator and a translating device supplied thereby, means for controlling the field-strength ol' the generator" to vary the voltage supplied to said device, and means for connecting the generator field in shunt to its armature to reduce the generator voltage to zero.

4:. In combination with a generator and a translating device supplied thereby, a separate source of current. (or the generator tield, means for varying the current supplied by said source to the tield, and means for disconnecting the iield from said source and connecting it in shunt lo the generator armature to annihilate the generator voltage due to residual magnetism.

5. In combination with a generator and a translating device supplied thereby, a separate source of current. and a controlling switch adapted to connect the generator lield to said son to vary the amount: olf current supplied to the held by ..aid source, and in its oil-position to dis-com ncct the field from said source and to connect it in shunt to the generator armature In witness whereof, I have hereunto set my hand this Ld day 01 January. 1907.

(,llCOltt} STERN.

Witnesses Hnixiacu llrsenaxz, AL'uUs'r Ilia-nu. 

